Aromatic polyesters represented by polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) have excellent mechanical properties, chemical resistance, and electrical characteristics. Furthermore, reinforcement with a filler can impart the rigidity and heat resistance to the aromatic polyesters. Such aromatic polyesters are used in a wide range of fields such as automobiles, home appliances and OA. However, filler-reinforced polyesters have drawbacks that a product appearance is impaired when an additive amount of the filler increases, and warpage generates easily when an additive amount of the filler is small, and scratch resistance is low when the polyesters are used as the parts which need appearance.
As a means to improve appearance and warpage of a molding, a method of blending a polyethylene terephthalate with a composition that contains a filler-reinforced polybutylene terephthalate and a styrene-based resin (Refer to patent document 1), and a composition that contains a filler reinforced-polytrimethylene terephthalate and a thermoplastic composition (Refer to patent document 2) have been reported.
It has been well-known that the composition composed of these aromatic polyesters and styrene-based resin varies greatly in the physical properties depending on the compatibility, the viscosity and the volume ratio. Among them, especially the compatibility largely effects a change in the physical properties. However, a styrene-based resin, which has been used heretofore in the composition with an aromatic polyester and contains 20-30 mass % of an unsaturated nitrile-based monomer, whose compatibility with aromatic polyesters is relatively high, has the problems of lowering the degree of crystallinity of polyesters, lowering the heat resistance, and the like.
As a composition to solve the above problems, a resin composition comprising an aromatic polyester and two kinds of styrene-based resins, in which a ratio of an unsaturated nitrile-based monomer is from 10 to 50 mass % and the ratio is different, has been reported. The composition composed of these components shows imperfect crystallinity, therefore, an adhesion reducing agent is blended, and thus, the deposition due to the adhesion reducing agent can be decreased by extremely reducing the blending amount, and shortening of the molding cycle is enabled.    Patent document 1: JP-B-3098308    Patent document 2: JP-A-2003-20389    Patent document 3: JP-A-2003-503574